This invention relates to array antennas suitable for cellular use and, more particularly, to such antennas employing a single column of dipoles with inclusion of slot radiating elements extending through a reflector to re-radiate behind the antenna, providing signal cancellation to improve front-to-back performance.
With the expansion of cellular and other wireless communication services, there is a growing requirement for antennas suitable for communication with cellular telephones and other mobile user equipment. These antennas are typically provided in fixed installations on buildings or other structures in urban and other areas. The characteristic of the use of a large number of contiguous cell coverage areas of relatively small size, particularly in urban installations, results in the need for installation of large numbers of antennas. The need to provide reliable communications service to a population of users moving through coverage areas with varying transmission characteristics places special requirements on the antennas.
While many types of antennas are available for these applications, where narrower beamwidths are required prior antenna designs have typically resulted in antennas of undesirable size, particularly as to reflector width, or antenna front-to-back thickness, or both. For example, where it is desirable to provide a 90 degree azimuth beamwidth by use of a single vertical column of dipoles, a relatively wide and/or thick antenna construction has typically been necessary, in order to achieve the desired beamwidth while limiting back radiation (e.g., achieving a front-to-back ratio of the order of 25 dB). For a 90 degree beamwidth, prior art techniques may typically result in an antenna 12 inches wide and 12 inches deep.
Thus, while desired operating characteristics may be achieved in prior antennas by combinations of a wide reflector behind a stack of active and cooperative inactive elements, for example, optimum size reduction is not achieved. Antenna size is a significant consideration with respect to overall obtrusiveness of antenna installations, as well as wind loading, weight, etc. As will be appreciated, larger antennas result in increased wind loading forces, increased weight, increased lateral space requirements where a plurality of antennas are mounted at one site, etc. Greater requirements as to structural strength and capacity potentially increase the size and cost of towers and other antenna mount structures.
Objects of the invention are, therefore, to provide new and improved cellular antennas and such antennas characterized by one or more of the following:
improved front-to-back performance, PA1 use of slot radiating elements extending through reflector portions, PA1 cancellation of signals otherwise radiated behind an antenna, and PA1 narrow reflector width, while achieving desired performance characteristics, such as front-to-back ratio.